Montenegro's premier expressed optimism Thursday that the tiny Balkan country would join NATO by the year's end, after the chief of the military alliance visited Podgorica and commended its reforms.

At the end of a two-day visit by NATO Secretary General Jens Stoltenberg, Prime Minister Milo Djukanovic said he was "full of optimism... that Montenegro hopefully will be invited to join NATO as early as in December".

A formal decision on Montenegro's membership bid is to be made at a meeting of NATO foreign ministers in early December.

Stoltenberg, who said he would "not prejudge the decision", commended Montenegro for reforms and said it was "taking the right steps" towards their implementation, which was key to NATO membership.

"Montenegro has already introduced substantial reforms. You are making an important progress in strengthening the rule of law and I encourage you to further build public support for membership," Stoltenberg said.

After breaking away from a loose alliance with Serbia in 2006, the Adriatic nation of around 630,000 people announced its desire to join the 28-member NATO bloc.

It received a boost last month when the United States came out in favour of supporting Montenegro's accession.